1. Field of the Invention
The present invention relates to a real image finder optical system of a camera, which includes a relay lens system, and which is formed separately from the photographing optical system.
2. Description of the Related Art
A real image finder optical system having a relay lens system has been known. The conventional real image finder optical system comprises a positive objective lens system (the first lens group), a positive relay lens system (the second lens group), and an eyepiece lens system (the third lens group), in this order from the object side. In this finder optical system, an inverted primary image of an object is formed through the positive objective lens system, an erected secondary image is formed through the positive relay lens system, and the erected secondary image can be viewed through the eyepiece lens system.
In the above real image finder optical system, aberrations, such as spherical aberration and comatic aberration, occur due to strong positive power of each lens group. Furthermore, field curvature increases due to the Petzval sum being increased.
In the conventional real image finder optical system having a relay lens system, the above-mentioned aberrations are corrected firstly by providing a positive and a negative lens elements, which are respectively formed from lens materials of different dispersive powers. In addition, options, such as increasing the number of lens elements and/or using a lens material of a high refractive index and low dispersive power, can be taken. However, such a lens structure incurs a high cost.